NRF2-mediated Notch pathway activation enhances hematopoietic reconstitution following myelosuppressive radiation

A nuclear disaster may result in exposure to potentially lethal doses of ionizing radiation (IR).Hematopoietic acute radiation syndrome (H-ARS) is characterized by severe myelosuppression, which increases the risk of infection, bleeding, and mortality.Here, we determined that activation of nuclear factor erythroid-2-related factor 2 (NRF2) signaling enhances hematopoietic stem progenitor cell (HSPC) function and mitigates IR-induced myelosuppression and mortality.Augmenting NRF2 signaling in mice, either by genetic deletion of the NRF2 inhibitor Keap1 or by pharmacological NRF2 activation with 2-trifluoromethyl-2′-methoxychalone (TMC), enhanced hematopoietic reconstitution following bone marrow transplantation (BMT).Strikingly, even 24 hours after lethal IR exposure, oral administration of TMC mitigated myelosuppression and mortality in mice.Furthermore, TMC administration to irradiated transgenic Notch reporter mice revealed activation of Notch signaling in HSPCs and enhanced HSPC expansion by increasing Jagged1 expression in BM stromal cells.Administration of a Notch inhibitor ablated the effects of TMC on hematopoietic reconstitution.Taken together, we identified a mechanism by which NRF2-mediated Notch signaling improves HSPC function and myelosuppression following IR exposure.Our data indicate that targeting this pathway may provide a countermeasure against the damaging effects of IR exposure.Augmenting NRF2 signaling by genetic disruption of Keap1 improves HSPC function under steady-state conditions.(A) mRNA expression of Keap1 and NRF2-regulated genes Nqo1 and Gclm in BM cells isolated from poly(I:C)-treated MxCre-Keap1 flox/flox mice and floxed controls.*P < 0.05; **P < 0.01; ***P < 0.001.RFC, relative fold change.(B-F) Flow cytometric analysis (B), percentage (C), and absolute number of LSK cells (D).Percentage (E) and absolute number (F) of HSCs and MPP cells in BM from MxCre-Keap1 flox/flox mice and floxed controls following poly(I:C) treatment under baseline conditions.MxCre-Keap1 -/-is represented as Keap1 -/-in the graph legends.*P < 0.05, **P < 0.01, and ***P < 0.001 compared with respective floxed controls (n = 10-12).(G) CFU/200 LSK cells from MxCre-Keap1 -/-mice and floxed controls.*P < 0.05; **P < 0.01.BFU-E, erythroid burst-forming units; M-CFU, megakaryocyte CFU.